Mineral fillers, such as calcium carbonate, are commonly added to a plastic material (such as unsaturated polyester resins) to provide reinforcement, increase hardness and to lower overall formulation cost. Other mineral fillers, such as alumina trihydrate, which endothermically decompose upon heating to liberate water, are known to have a flame retardant effect in plastic materials such as unsaturated polyester composites. However, adding a significant amount of filler the overall viscosity of the system generally increases. Dispersing agents are commonly used to wet out the dry filler during mixing, reduce the viscosity and make the formulation more workable. Phosphate esters are highly effective dispersing agents but they cannot be used in hand- and spray-lay-up applications due to interference with the curing mechanism.
Such reinforced plastic material as referred above, comprising a plastic material, filler and a dispersant are used in the industry as material for yacht interiors, boat hulls, wind turbines, train interiors and the like. The required plastic/filler/dispersant composition is generally placed into a mould and set. The addition of more filler to the composition with respect to the plastic material, cheapens the cost. However, if too much filler is added to the mix, the composition becomes too viscous and harder to work.
Fillers not only reinforce the plastic for added strength, they can also offer other advantages. For example, a known filler, aluminium trihydrate is commonly used as a fire retardant filler. Upon heating of the plastic containing the fire retardant filler, the aluminium trihydrate decomposes to release water, therefore preventing the material from catching fire.
A number of references disclose dispersants for media such as plastics are summarised below.
U.S. Pat. No. 5,300,255 discloses dispersants containing a polyester derived from a hydroxycarboxylic acid with not more than 8 carbon atoms reacted with phosphorus pentoxide or sulphuric acid. The dispersants are useful in non-polar media, such as aromatic solvents and plastics.
U.S. Pat. No. 5,130,463 discloses dispersants containing a polyether/polyester derived from ε-caprolactone reacted with polyphosphoric acid.
U.S. Pat. No. 6,051,627 discloses dispersants including a polyether derived from ethylene oxide and propylene oxide reacted with polyphosphoric acid.
U.S. Pat. No. 4,281,071 discloses the use of an organo-phosphite for viscosity reduction of filled unsaturated polyester resin compositions.
Non-phosphate dispersants are disclosed in U.S. Pat. No. 3,332,793. U.S. Pat. No. 3,332,793 discloses suspending agents based upon carboxylic acid-terminated polyether/polyester chains subsequently reacted with a polyamine.
A number of documents disclose methoxy polyethylene glycol esters of polyacrylic acids and their use as dispersants.
EP 2 065 403 A discloses a process for making methoxy polyethylene glycol esters of polyacrylic acid, and their salts, as dispersants for gypsum, cement, and pigments in aqueous systems.
EP 1 061 089 A discloses methoxy polyethyleneglycol esters of polyacrylic acid, modified with organic amines, as cement super-plasticisers.
U.S. Pat. No. 5,840,114 discloses a methoxy polyethyleneglycol ester and methoxy polyethyleneglycol amide of a polycarboxylic acid prepared by direct esterification/amidation.
U.S. Pat. No. 5,476,885 discloses methoxy polyethyleneglycol esters of poly(meth)acrylic acids prepared from the reaction of the methoxy polyethyleneglycol with (meth)acrylic acid.
German Patent DE 3 325 738 discloses products made by the direct esterification of polyacrylic acid with C16-18 alcohol ethoxylates.
There are 2 commonly known processes for polymerizing plastics material. The first method is that of heat curing. Heat curing involves the heating of the reaction mixture in order to initiate polymerization. In the heat cure process, phosphates are added as dispersants as they are highly efficient at lowering the viscosity of a plastic material/filler mix.
The second method is that of curing at an ambient temperature. At an ambient temperature, the reaction is initiated by metal initiators, commonly cobalt complex activators.
Dispersants are commonly used in unsaturated polyester composites to incorporate high levels of mineral fillers effectively whilst maintaining a workable viscosity.
In ambient temperature cure systems the cross-linking reaction, using a peroxide radical source, is initiated by the use of cobalt complex activators. The cross linking reaction involves the linking of unsaturated polyesters to form chain polymers through polymerization. It is before this stage of the process that fillers and dispersants are added to the mixture.
The use of cobalt as a mineral catalyst is commonly used, however, other promoters are also used such as copper, manganese, zinc, zirconium and iron, when a cobalt free system is required. Such promoters can be used in conjunction with dimethylaniline, which has an effect of shortening the cure time of the polymerization process.
However, in ambient cure processes, phosphates cannot be used as dispersants.
Strongly acidic dispersants, such as phosphate esters, bind to such cobalt initiators and delay or prevent the cross-linking reaction from taking place.
Consequently there is interest in alternative chemistries to provide effective dispersants in such systems which will not interfere in cross-linking reactions.
GB 887 241 discloses a range of dispersing agents designed for use in ambient-cure composites. These products, based upon polyether-polyester chains as a salt with a polyamine, have a good effect on wetting fillers, with only a minimal effect on cure retardation. However the dispersants disclosed are inefficient as they comprise a single anchor group in the chain, therefore a high quantity of dispersant is needed to reduce the viscosity of a filler/plastic material mix.
Mineral fillers, such as calcium carbonate, are commonly added to unsaturated polyester resins to provide reinforcement, increase hardness and to lower overall formulation cost. Other mineral fillers such as alumina trihydrate, which endothermically decompose upon heating to liberate water, have a flame retardant effect when used as filler in unsaturated polyester composites. The adverse effect of adding a significant amount of filler is that the overall viscosity of the system increases. Dispersing agents are commonly used to wet out the dry filler during mixing, reduce this viscosity and make the formulation more workable. Phosphate esters are highly effective dispersing agents in a heat cure process but they cannot be used in hand and spray-lay-up applications due to interference with the curing mechanism.
During a cure process, unsaturated polyesters, which are supplied as a solution in styrene or other reactive monomer, are cured by a radical mechanism, initiated by an organic peroxide such as methyl ethyl ketone peroxide. The radicals thus created crosslink the double bonds in the polyester resin with the double bonds in the styrene diluent, forming a rigid 3-dimensional network. The starting point of the reaction is the decomposition of the organic peroxide, which can be initiated using a heated mould (heat-cure) or by using an organo-cobalt compound dissolved in the resin (ambient or cold cure).
Many dispersing agents for use in these systems are based upon phosphate esters. Phosphate groups bind tightly to basic filler surfaces, thus giving effective wetting and viscosity reduction. They also, however, bind tightly to the cobalt compound, thus inhibiting the breakdown of peroxide and retarding the cure of the composite. Consequently phosphated dispersants cannot be used in metal activated ambient-cured systems.
None of the known dispersants as disclosed herein are able to control the rate of curing and furthermore there is a need for a dispersant that can be used in an ambient cure system and have a high dispersant activity with respect to lowering the viscosity of a plastics/filler mix therefore, enabling an increase in filler to be added to a plastics material, therefore lowering manufacturing costs.